1. Field
One embodiment of the present invention relates to an optical system, exposure apparatus, and exposure method and, more particularly, to an exposure apparatus for fabricating micro devices, such as semiconductor elements, image pickup devices, liquid-crystal display devices, and thin-film magnetic heads, for example, by lithography.
2. Description of the Related Art
In the typical exposure apparatus of this type, a light beam emitted from a light source is guided through a fly's eye lens as an optical integrator to form a secondary light source as a substantive surface illuminant consisting of a lot of light sources. A light beam from the secondary light source is guided through an aperture stop disposed in the vicinity of the rear focal plane of the fly's eye lens, to be limited, and then is incident to a condenser lens.
The light beam condensed by the condenser lens illuminates a mask with a predetermined pattern therein, in a superposed manner. Light transmitted by the pattern of the mask travels through a projection optical system to be focused on a wafer. In this manner the mask pattern is projected (or transferred) onto the wafer to effect exposure thereof. The pattern formed in the mask is of high integration and a high-contrast pattern image must be formed on the wafer in order to accurately transfer the microscopic pattern onto the wafer.
Japanese Patent Application Laid-Open No. 5-90128 proposed technology of obtaining the high-contrast image of the microscopic pattern on the wafer, for example, by setting a polarization state of exposure light to linear polarization of circumferential vibration (hereinafter referred to as “azimuthal (circumferential) polarization state”) in a lens aperture (pupil plane) of the projection optical system.